1. Field of the Invention
This invention relates to seat belt retractors for passengers in vehicles such as automobiles, and more particularly to an inertia responsive safety belt retractor which is vehicle sensitive, that is to say, one responsive to acceleration of the vehicle, for preventing protraction of the belt upon predetermined acceleration of the vehicle.
2. Description of the Prior Art
Vehicle sensitive safety belt retractors have been recently developed which should significantly decrease the number of fatalities and serious injuries resulting from motor vehicle accidents. Most of these retractors include a belt reel which is continually biased in a retracting direction, a pawl which is engageable with ratchet teeth on the end or associated with the belt reel, and an actuating mechanism having a pendulum in contact with the pawl and freely suspended from a ball and socket type mount. When the pendulum is displaced from its normally vertical position by an acceleration of the vehicle, it moves the pawl into engagement with the ratchet teeth, preventing further protraction of the belt. It is obviously of prime importance that the force necessary for proper displacement of the pendulum from the vertical position be correctly established and maintained at the magnitude necessary for proper actuation of the pawl. This requirement has, however, been difficult to meet. Particles of dirt and corroded material entrapped between the ball and the socket, as well as the sliding friction generated therebetween, can alter the acceleration required to displace the pendulum by a magnitude as high as one hundred percent or more. Unless regularly serviced, the actuating mechanism of the retractor may become insufficiently reliable in operation when subjected to changing climatic conditions for prolonged periods of time. For the above reasons, retractors of the type generally described result in lower reliability factors and higher maintenance costs than are considered to be commercially acceptable.
Retractors have also been designed in which an inverted pendulum moves between two stable positions on the occurrence of acceleration force sufficient to lock the retractor and on cessation of those acceleration forces. Such a retractor is shown, for example, in U.S. Pat. No. 3,758,044. Such structure of the prior art suffers, among other deficiencies, from a complexity of operating structure and from the transience of the locking ability (the automatic) return of the inverted pendulum to the unlocked position on cessation of the acceleration force).